I. Field of the Invention
The present invention is directed generally to the field of high energy density, non-aqueous active metal electrochemical cells and, more particularly, to an unique interspersed expanded metal collector grid for use as an anode substrate in support of the active metal of the anode for such a cell to improve reliability and facilitate manufacture.
Il. Description of the Related Art
Active metal cells of the class described, typically consist of a light, strongly reducing active anode material, normally an alkali metal such as lithium, an aprotic, non-aqueous solvent depolarizer such as thionyl chloride or sulfur dioxide into which an appropriate quantity of a salt of the anode metal such as LiA.sub.5 F.sub.6 or LiBF.sub.4 has been dissolved to form a conductive solution, and an oxidizing agent as the cathode active material.
In some applications, the cells are assembled as deferred action or reserve cells in which the electrolyte system is typically stored separated from one or both electrodes contained in a readily rupturable container such as a glass ampule such that the cells remain in an inactive state until such time as the cell is activated. Activation is normally accomplished by applying an external force in a predetermined manner to rupture the glass ampule thereby allowing rapid dispersal of the electrolyte system to complete the electrochemical continuity between anode and cathode. In other applications, the cells are manufactured and assembled in the active state in which the electrolyte system is supplied at the time of assembly giving the cell complete electrochemical continuity from the beginning. Some active cell configurations may also be rechargeable with respect to redepositing the active metal of the anode after discharge or partial discharge of the cell in a cyclical manner.
Generally, all of the above-mentioned types of cell applications have substantially common fundamental construction with respect to anode, cathode and separator. In one configuration, the active metal anode material is carried by an anode current collector support member in the form of a stainless steel or nickel expanded metal or wire mesh. Thin layers of the anode active material are applied over one or both faces of the gridwork and pressed firmly into the grid by a laminating roller. A layer of separator material, which may be paper or ceramic, is disposed between the anode support member carrying the anode active material and a cathode collector member, usually nickel, which carries the cathode active material, usually carbon or acetylene black. Teflon or other such binder material may be used to help adhere the carbon black to the cathode collector member.
The anode support member carries the anode lead which is normally a solid conductor member. In the past, these leads have been attached to the expanded metal of its collector member by welding the expanded metal grid to the solid lead. This prior technique was not reliable enough with respect to achieving uniform weld strengths and it was "hit and miss" as to whether any particular welded lead was properly attached.
In addition, the welding of the lead to the expended metal often resulted in an undesirable amount of metal build-up in the vicinity of the lead attachment. This produced further problems with the laminating process because of the increased unevenness or nonuniformity of the thickness of grid support layer in the area of the lead attachment. In certain cases, the build-up has been enough such that when the layers including the separator barrier and the composite cathode are assembled with the anode into a thin composite, electrode shorting could occur in the finished product.